I have been using Inquisitor in Safari for quite sometime and enjoy its slick interface and ease of use. Recently, info was released regarding its next incarnation, Inquisitor 2.0 which looks very promising.

I must say that the Inquisitor Instant Search Beta is an online version of the same search interface, working on any platform. Built on the same technology that powers Google Suggest with some AJAX goodness, should prove to be an interesting experiment.